The present invention relates to powerline networking and, more particularly, to enhanced power saving methods and systems for a powerline network.
Powerline networks provide entertainment-oriented networking by supporting communication of video, audio and data content over alternating current (AC) wiring within dwelling units. One industry document that governs powerline networks is the HomePlug AV (HPAV) specification. An HPAV network operates on a single physical channel and may include one or more audiovisual logical networks (AVLN). Each AVLN has one or more nodes and is managed by a central coordinator (CCo) entity that is active on a managing one of the nodes. Each AVLN is assigned a different network membership key (NMK) that enables nodes within the AVLN to encrypt and decrypt information transmitted within the AVLN and prevents nodes outside the AVLN from snooping such information.
Communication in an HPAV network is achieved by transmitting and receiving information on the channel in successive beacon periods. The beacon periods are synchronized to the AC line cycle, with each beacon period traversing two cycles. Turning to FIG. 1, within an exemplary beacon period 100 there is a beacon region 110, a shared carrier sense multiple access (CSMA) region 120 and a reserved region 130. The managing node of an AVLN advertises control information, such as a transmission schedule, to the nodes in its AVLN in a beacon slot 140 within beacon region 110. Beacon region 110 is followed by shared CSMA region 120 in which nodes in all AVLN may attempt contention-based communication on a priority or “best effort” basis. Shared CSMA region 120 is followed by reserved region 130 in which nodes that have been allocated time slots by a managing node may engage in contention-free communication. In some implementations, the beacon period does not include a reserved region.
In known HPAV networks, all nodes monitor the channel in the shared CSMA region of each beacon period. However, if there are no packets to transmit, having all nodes monitor in the shared CSMA region can waste power. The amount of wasted power can be considerable when the HPAV network is idle for a long time, such as in the late evening hours when the users of the network are typically asleep. To improve power conservation, the HPAV specification defines a basic power saving mode called network power saving mode (NPSM). In NPSM, if a managing node of an AVLN does not detect a valid transmission on the channel for at least 30 seconds, the managing node sets an NPSM bit in the next beacon slot for the AVLN and announces a schedule consisting only of the beacon region, a shared CSMA region of minimum length (e.g. 1500 milliseconds) and a reserved region of sufficient size to support discover and proxy beacons. The managing node designates the rest of the beacon period a stayout region which nodes in the AVLN do not monitor, allowing them to enter a power conserving “sleep” mode. Turning to FIG. 2, for example, while NPSM is active, after transmission of a beacon 210 and an interframe space a shared CSMA region 200 begins in which nodes monitor the channel and may indicate that they have a packet to transmit by sending one or more priority resolution symbols (PRS) in priority resolution symbol slots (PRS0 SLOT, PRS1 SLOT) 220, 230. If the nodes do not detect a valid transmission within a minimum shared CSMA region (MIN CSMA REGION) that includes PRS slots 220, 230 and an additional window 240, the nodes suspend monitoring of shared CSMA region 200. On the other hand, if a valid transmission is detected within the minimum shared CSMA region, NSPM terminates and the nodes monitor the entire shared CSMA region 200, even after all packets have been transmitted.
Unfortunately, NSPM is not very energy efficient. In NSPM, at least a 30-second idle period passes before the managing node sets the NSPM bit. Still more time passes before the minimum shared CSMA region passes without a valid transmission and the nodes suspend monitoring. And if a valid transmission is detected within the minimum shared CSMA region, NPSM terminates and the nodes monitor the entire shared CSMA region even after there are no more packets to transmit.